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標題: | Lacosamide抑制鈉離子通道之分子機制 The mechanisms underlying the inhibitory effect of lacosamide on the voltage-gated sodium channels |
作者: | Yi-Shuan Peng 彭奕璇 |
指導教授: | 郭鐘金(Chuan-Chin Kuo) |
關鍵字: | 癲癇,鈉離子通道,快速不活化態,慢速不活化態, epilepsy,anticonvulsant,sodium channel,lacosamide,phenytoin,lidocaine,fast inactivation,slow inactivation, |
出版年 : | 2019 |
學位: | 碩士 |
摘要: | 在以往的研究中已充分顯示,誘發神經興奮與動作電位的傳導主要是由電壓依賴型鈉離子通道所控制。當腦部產生異常的神經興奮時,會使得神經元過度興奮並產生類似癲癇的一些神經疾病。然而這些病患在臨床上的治療方式主要是給予典型的抗癲癇藥物,像是carbamazepine、phenytoin、lamotrigine等會去抑制電壓依賴型鈉離子通道開啟,使得興奮減少,達到治療效果。而這些典型的抗癲癇藥物也已經被證實是透過緩慢地結合在鈉離子通道的快速不活化態(fast inactivation state),並且相對於休息態(resting state)的鈉離子通道,藥物更容易結合在鈉離子通道上的快速不活化態。另外,在近十多年的研究中,也發現到lacosamide (LCM)這一種較為新穎的抗癲癇藥物,而這種藥物又與典型傳統抗癲癇藥物有所不同,被認為可能會選擇性的結合到鈉離子通道的慢速不活化態(slow inactivation state)。本篇論文首先探討,LCM抑制鈉電流的效果,量化其濃度依賴性及電壓依賴性,在不同電壓下LCM的抑制效果,可由一對一結合曲線描繪。並得到在-70 mv,LCM對於鈉離子通道的直觀解離常數(KI)約為150 µM。其次再由LCM對鈉離子通道的脫離速率與結合速率常數所得的比值,也得到相似的KI (約155 µM,-70mV)。而在不同濃度的LCM對電壓依賴不活化曲線的位移中,所得到KI值約為156 µM。因此可得知LCM對於不活化態之鈉離子通道的親和力約為150-156 µM,遠大於休息態的鈉離子通道(>10 mM)。另外,我們也利用等差電壓下給予不同時間(100毫秒或18秒)的去極化,並繪製出快速不活化曲線、慢速不活化曲線及快慢速混合不活化曲線,測出LCM主要是結合在鈉離子通道的慢速不活化態。再者,也比較給予長時間-80 mV或-10 mV的去極化,LCM對鈉離子通道相較控制組皆有較慢回復至休息態的趨勢,其中又以後者較為顯著,這也支持LCM對鈉離子通道慢速不活化態的作用大於快速不活化態。我們也針對新型藥物LCM、典型藥物phenytoin以及局部麻醉劑lidocaine做一個比較,並將兩種藥物混合使用(lacosamide+phenytoin & lacosamide+lidocaine)看是否能因為藥物作用的途徑不一樣而達到藥物加成效果。結果發現LCM及phenytoin混合後,其對鈉離子通道的抑制效果更為明顯,但在快速與慢速不活化態有不一樣的加成效果,而LCM及lidocaine混合後,其對鈉離子通道的抑制效果也更為明顯,而且至少在快速不活化態中有達到互助加成(synergistic)效果。 It has been shown that the genesis of nerve excitation and action potential conduction is mainly controlled by voltage-gated sodium channels. Abnormal neuronal excitation may lead to neurological disorders like epilepsy. The sodium channel inhibitors such as carbamazepine, phenytoin, lamotrigine, have been the mainstay of medical treatment of epilepsy. These prototypical anticonvulsants have been shown to bind to the fast-inactivated state rather than resting state of the sodium ion channel. Lacosamide (LCM) is a new generation anticonvulsant, which also inhibits sodium channel but is different from the prototypical ones. The molecular actions of LCM on sodium channels are not clear, although selective binding to the slow-inactivated state of the sodium channel was proposed. We found that LCM dose-dependently inhibits sodium currents at more depolarized holding potentials, and the inhibitory effect could be described by different one-to-one binding curves at different holding potentials, giving an apparent dissociation constant (KI) of ~ 150 μM at -70mV for LCM binding to the inactivated sodium ion channels. The apparent dissociation constant derived from the ratio between the binding rate constant of LCM and the unbinding rate from the sodium channel is ~155 μM (at -70mV). In addition, a KI of ~156 μM is derived from the LCM concentration-dependent shift of the inactivation curve. The apparent dissociation constant of LCM for the sodium channel of the inactive state is therefore about 150-156 μM, which is much smaller than that for the resting sodium channels (>10mM). On the other hand, different inactivation curves are constructed with 100 milliseconds or 18 seconds inactivating pulses at various voltages (fast inactivation curves, slow inactivation curves and “combined’’ inactivation curves) to show that the very slow kinetics of LCM action on the inactivated sodium channels. Furthermore, LCM slows recovery from the inactivated to the resting state. The slowing effect is much more manifest with inactivating pulse at -10 than -80 mv, indicating that the effect of LCM on the slow-inactivated sodium channels is greater than on the fast-inactivated state. Last but not the least, we also explored the effect of concomitant LCM and phenytoin & LCM and lidocaine on sodium currents, and found that the LCM and phenytoin have a different action on the fast inactivation and slow inactivation of sodium channels; however, LCM and lidocaine have a synergistic inhibitory action on fast inactivation of the sodium channels. |
URI: | http://tdr.lib.ntu.edu.tw/jspui/handle/123456789/73937 |
DOI: | 10.6342/NTU201901556 |
全文授權: | 有償授權 |
顯示於系所單位: | 生理學科所 |
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